Such air-bulking devices with a threading slot that is constantly open to provide for simple handling have been known in various designs.
In recent years, the requirements to be met by air-bulking devices for smooth yarns, preoriented yarns (POY yarns), fully oriented yarns (FOY yarns) and fully drawn yarns (FDY yarns) have greatly increased due to a growing usage of filament yarns with ever finer individual filaments. The finer monofilaments require, for troublefree further processing, an improved compactness of the thread with a minimum of projecting filament loops, meaning for the air-bulking of these filament yarns a requirement for increasingly shorter opening lengths between the air-bulk knots. This means, at the same time, that the air-bulking density, measured as the number of air-bulk knots or fixed points per meter of yarn length (FP/m), must be raised to ever higher values.
It is an object of the invention to fashion the above-discussed device in such a way that the required high air-bulking density can be attained at a high uniformity of the fixed point spacings--without the occurrence of individual larger fixed point spacings or opening lengths--and with a very low blowing air consumption per air-bulk knot.
This object has been achieved according to the invention by the combination of features indicated in the characterizing portion of claim 1.
Individual features have been known per se in air-bulking devices. Thus, a person skilled in the art knows that air-bulking devices having predominantly round (cylindrical) yarn channels are suitable for low to medium air-bulking densities but that, for higher air-bulking densities, air-bulking devices are utilized with yarn channels exhibiting usually a planar impingement surface for the blast jet from the blast nozzle and even including, in part, up to three planar surfaces.